Abstract

High concentrations of soil Al³⁺ in acid soil severely influence the growth of Medicago sativa (alfalfa). The objective of the current study was to analyze whether Arbuscular Mycorrhizal Fungi (AMF) inoculation could improve alfalfa growth in acid soils. A two-way completely randomized factorial design was employed for M. sativa and M. lupulina (black medick) with two inoculations (rhizobia and AMF) and three Al³⁺ levels, and replicated four times. The soil Al³⁺ levels were adjusted to 900 mg/kg, 1000 mg/kg and 1100 mg/kg. Spores of AMF were isolated directly from rhizosphere soils of black medick. The rhizobia were isolated from root nodules in fields separately from two plant species. At each Al³⁺ level, there were four inoculations, non-inoculation, AMF solely, rhizobia solely and dual-inoculation with AMF and rhizobia. Soil Al³⁺ concentration significantly limited above- and below-ground growth of both alfalfa and black medick, reducing plant height, branching number, shoot and root weight, and root length, surface area and volume. Compared to rhizobia, AMF showed a higher tolerance to soil Al³⁺. AMF inoculation increased the shoot and root weight of both plant species under most circumstances. Overall, AMF colonization had a trend in increasing the contents of phosphorus in both plant species at all Al³⁺ concentrations but not nitrogen and potassium. Dual inoculation significantly increased nodulation ability, enabling both plant species to form nodules at 900 and 1000 mg/kg Al³⁺. Though the soil Al³⁺ concentration influenced the efficiency of AMF inoculation, AMF inoculation improved nodulation, increased plant growth and nutrient uptake, suggesting that it was an alternative way in improving alfalfa growth in acid soils.

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